I'd mirror
jrielley's comments.
If you have a PM you don't need a smart trainer. If you don't have a PM but do have a dumb trainer that's stable with well modelled virtual power you can also enjoy Zwift without needing to invest in a smart trainer.
I use a KK Road Machine with Zwift (no PM) and find it very enjoyable and hugely beneficial compared to non-Zwift trainer sessions which I'd used but hated prior to starting Zwifting in Oct 2016. There is some additional uncertainty about the accuracy of your power figures but repeatability is good and that's the most important thing. Many other trainers are not nearly as good and may may not be realistic options without a PM (Cyclops Fluid 2 for example which dramatically changes resistance as the fluid temperature changes).
The benefits of a smart trainer are:
- Terrain simulation (resistance varies to reflect the gradient of the virtual road)
- ERG mode (trainer controls power at a pre-determined level so long as you can keep the pedals turning which allows you execute programmed workouts without watching the power numbers)
Terrain simulation would be nice, I don't find it essential on the trainer or on Zwift. It's absolutely usable without it.
ERG mode holds no attraction for me. I've tried it and do not like it. Besides, STers do like to talk about the benefits of specificity, which seems at odds with using ERG. Surely the mental aspect of modulating power for yourself is relevant?
Give Zwift a go. Don't they still do a free trial? It's made a huge difference to my cycle training both in terms of enjoyment and performance. Some people don't seem to like it, in which case just ditch it again and don't pay.